Alfisols
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Alfisols are a soil order in USDA soil taxonomy. Alfisols form in semiarid to humid areas, typically under a hardwood forest cover. They have a clay and nutrient-enriched subsoil. "Alf" refers to aluminium (Al) and iron (Fe). Because of their productivity and abundance, the Alfisols represent one of the more important soil orders. They are widely used both in agriculture and forestry and are generally easier to keep fertile than other humid-climate soils, though those in Australia and Africa are still very deficient in nitrogen and available phosphorus. Those in monsoonal tropical regions, however, have a tendency to acidify when heavily cultivated, especially when nitrogenous fertilisers are used.
In the FAO soil classification, most Alfisols are classified as Luvisols or Lixisols, but some are classed as Nitosols.
Alfisols occupy around one tenth of the Earth's ice-free land surface. They are dominant in many areas, such the Ohio River basin in the United States, southern and unglaciated Western Europe, the Baltic region and central European Russia, the drier parts of Peninsular India, the Soudan in Africa, and many parts of South America.
Alfisols represent the youngest forest soil order. Because of this they are less leached, and have a greater than 35% base saturation. They are more weathered than inceptisols but less weathered than ultisols, unlike which they occur to the north of the limit of maximum glaciation in North America.
The fossil record of Alfisols begins in the Late Devonian. Alfisols, probably owing to their fertility, are the oldest forest soils: vegetation on weathered Oxisols, by contrast, is not known earlier than Middle Permian. Fossil Alfisols remain common from the Carboniferous and all periods since the Eocene.[citation needed]
[edit] Suborders
- Aqualfs — wet soils; aquic soil moisture regime
- Cryalfs — cold climate; frigid or cryic soil temperature regime
- Udalfs — humid climate; udic moisture regime
- Ustalfs — subhumid climate; ustic moisture regime
- Xeralfs — Mediterranean climate; xeric moisture regime
